In recent years, the heightened awareness of global environmental problems has resulted in considerable investigation of the application of various types of fuel cells to automobiles. Among the various types of fuel cells, solid oxide fuel cells (SOFC) exhibit high efficiency, and are the focus of much attention as potential vehicle power sources.
Solid oxide fuel cells (SOFC) use a solid oxide material with oxygen ion conductivity such as a stabilized zirconia or ceria-based solid solution as the electrolyte. Moreover, an air electrode and a fuel electrode that exhibit gas permeability are stacked on the opposing surfaces of the solid electrolyte to form a unit cell. Using the gas-impermeable solid electrolyte as a partition, a fuel gas such as hydrogen or a hydrocarbon is supplied to the fuel electrode side from externally, and an oxidant gas such as air is supplied to the air electrode side, thereby generating electricity. Besides hydrogen and hydrocarbons, reformed gases obtained by reforming all manner of liquid fuels are sometimes also used as the fuel gas.
In those cases where a solid oxide fuel cell is used in an automobile or the like, the peculiarities of the usage environment mean that the solid oxide fuel cell sometimes requires a simultaneous combination of high-output operation and high durability. For example, Patent Document 1 discloses an electrochemical cell that includes a solid electrolyte layer, a first porous electrode layer, a second porous electrode layer, and a conductive porous support for supporting these layers, wherein gas flow channels are provided through which a gas flows when the surface of the conductive porous support contacts the gas. The conductive porous support has portions of differing porosity, and those portions of differing porosity are configured so that the porosity is low at the upstream side of the gas flow channels in the gas flow direction, and high at the downstream side. By employing this type of configuration, in which the porosity is low at the upstream side of the gas flow channels and high at the downstream side, the performance and efficiency of the electrochemical cell can be enhanced.